Self-cancelling switches



Oct. 13,1970 w, H 3,534,313

- SELF-CANGELLING SWITCHES Filed Nov. 27, 1967 3 Sheets-Sheet 1 BMa......,.\..1..1.h ATTORNEYS W. D.HOLT

I SELF-CANCELLING SWITCHES Oct; 13, 1970 3 Sheets-Sheet 2 Filed Nov. 27,1 967 a/MWiM ATTORNEYS Oct. 13, 1970 w. D. HOLT 3,534,313

SELF-CANCELLING SWITCHES Filed Nov. 27, 1967 5 Sheets-Sheet 8 Y 261A 262 i 55 57 Z 5@ L 52 Z66 I A 3 ATTORNEYS United States Patent 3,534,313SELF-CANCELLING SWITCHES William David Holt, Colne, England, assignor toJoseph Lucas (Industries) Limited, Birmingham, England, a Britishcompany Filed Nov. 27, 1967, Ser. No. 685,802 Claims priority,application Great Britain, Dec. 13, 1966, 55,692/ 66 Int. Cl. H01h61/00, 71/16 US. Cl. 337-39 4 Claims ABSTRACT OF THE DISCLOSURE Athermally operable, self cancelling switch including a body and anoperating member mounted on the body for movement between an offposition and first and second on positions. The second on position beingbetween the first or position and the off position. Resilient means urgethe operator member towards the off position. First and secondbimetallic elements are carried by the operating member. Catch means areprovided for each bimetallic element for maintaining the operatingmember in its first and second on positions. When the switch is in thefirst on position current flows through the first bimetallic elementwhich upon suflicient heating flexes out of the path of its catch means.Upon release from the first on position the operating member and firstand second bimetallic elements are urged by the resilient means to thesecond on position wherein the second bimetallic element engages itsrespective catch means. Upon deflection of the second bimetal theoperating means is urged to the 011? position. The direction ofdeflection of the bimetallic elements is perpendicular to their path ofmovement from the first on position to the oil? position.

This invention relates to thermally operable self-cancelling switches.

A switch according to the invention includes a plurality of bimetallicelements, and means whereby the elements are heated sequentially todetermine the overall operating period of the switch.

One example of the invention is illustrated in the accompanying drawingswherein FIG. 1 is a sectional view of a self-cancelling switch in itsoff position, FIG. 2 is a view similar to FIG. 1 but showing the switchin its operative positions, FIG. 3 is a sectional view on the line 3-3in FIG. 2, FIG. 4 is a horizontal, sectional view of the switch of FIG.1, but also showing in dotted lines, the parts of the switch in theiroperative positions and deleting certain parts for illustrativeconvenience, and FIGS. 5, 6 and 7 are views similar to FIGS. 1, 2 and 3respectively of a modification.

Referring to the drawings, the switch includes a moulded synthetic resinbody 11 of open rectangular box like construction having side walls 12,end walls 13 and a base 14, the open end of the body 11 being closed inuse by a moulded operating member 15. The member 15 is for-medcentrally, with a pair of short integral posts 16 which engage elongatedvertical slots 17 in the side walls 12 of the body 11. The posts 1 6 areurged to the upper ends of the slots 17 by springs 18 housed in theslots 17. Thus, the member 15 is capable of rocking movement withrespect to the body 11 in addition to vertical movement as allowed bycompression of the springs 18.

The base 14 of the body 11 supports a pair of conductive terminals 19,21. The terminal 19 is of strip like form and includes a portion 19awhich extends upwardly from the base within the body 11 in contact withan end wall of the body 11 and a portion 19b which extends lownwardlyfrom the base 14 for engagement with a lead.

3,534,313 Patented Oct. 13, 1970 The terminal 21 includes a portion 21awhich extends upwardly from the base 14 and a portion 21b similiar tothe portion 19b which extends downwardly from the base 14 for engagementwith a second lead. The portion 21a of the terminal 21 is bifurcated andthe bifurcations are bent in opposite directions towards the side wallsrespectively of the body 11. The bifurcations are shaped to define aspaced pair of catches 22, 23 which are parallel with, but verticallyspaced from the base 14.

The member 15 is formed with a pair of downwardly extending spacedparallel lugs 24 which define between them a channel 25, within which isengaged the central portion of a spring 26. The spring 26 includes alimb 26a which engages the underside of the operating member 15 at oneside of the pivotal axis of the member 15 and a second limb 26b whichextends within the body 11 and engages the portion 19a of terminal 19 onthe other side of the pivotal axis of the member 15. The spring 26 issecured in the channel 25 by a conductive rivet 27 which passes throughthe lugs 24. The rivet 27 further serves to secure a pair of bimetalstrips 28, 29 to the lugs 24 respectively. The strips 28, 29 extendparallel with the walls 12 towards the base 14 of the body 11 and areelectrically interconnected with the spring 26 and consequently theterminal 19, by the rivet 27. The strips 28, 29 are formed at their freeends with inwardly turned latch portions 31, 32 and the springs are soarranged that when heated they will move towards the walls 12, away fromeach other.

The operation of the switch is as follows: the terminals 19, 21 areconnected in a circuit which it is required to energise for apredetermined time. In the off position of the switch the member 15 isurged by the spring 26 to a position in which the strips 28, 29 areurged against insulating stops 33 carried by the body 11 (FIG. 4) and sothe circuit between the terminals 19, 21 is not completed. In order toenergize the circuit the member 15 is pivoted against the action of thespring 26 and in so doing, the strips 28, 29 are flexed to allow theirportions 31, 32 to pass the respective catches 22, 23. At the limit ofthe pivotal movement of the member 15, the portion 32 of the strip 29engages behind the catch 22 and makes an electrical contact therewith;thereby completing the circuit from the terminal 19 through the spring26, the rivet 27 and the strip 29 itself to the terminal 21. As currentflows through the strip 29, it becomes heated and so bends towards thewall 12 thereby disengaging the portion 32 from the catch 22. When thecatch 22 and the portion 32 disengage, the spring 26 urges the member 15towards its off position, but movement of the member 15 to its 01fposition is arrested by engagement of the portion 31 of the strip 28with the catch 23. Thus the circuit between the terminal 19, 21 is nowmade through the strip 28 which in turn becomes heated to allow theswitch to return to its off position. The switch therefore cancelsitself after a predetermined time, dependent on the sum of the operatingtimes of the two strips 28, 29.

If it is required to cancel the switch manually, the member 15 ispressed downwardly against the action of the springs 18 so that theportions 31, 32 of the strips 28, 29 ride under the catches 22, 23 andthe switch is returned to its off position.

In the modification shown in FIGS. 5, 6 and 7, the springs 18 areomitted and the diameter of the posts 16 on the member 15 and the widthof the slots 17 in the side walls 12 of the body 11 are increased and aslotted plate 34 is interposed between the member 15 and the base 14 ofthe body 11. The plate 34 is hinged at one end 35 to one end wall 13 ofthe body 11 while the other end of the plate 34 is urged towards themember 15 by a spring 36. The plate 34 includes a pair of laterallyspaced depressions 37 which engage the posts 16, the strips 28, 29extending through the slot in the plate 34. Thus when it is required tomanually cancel the switch, the member 15 is depressed to pivot theplate 34 against the action of the spring 36 so that the portions 31, 32of the strips 28, 29 can ride under the catches 22, 23 as the switch isreturned to its off position by the spring 26.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. A thermally operable, self-cancelling switch including a body, anoperating member mounted on said body for movement between an oifposition and first and second on positions, resilient means urging saidoperating member towards its ofi position, first and second terminalmembers carried by said body, first and second bi-metallic elementscarried by said operating member, and first and second catch meansassociated with said first and second bi-metallic elements respectivelyfor maintaining said operating member in its first and second onpositions respectively, the arrangement being such that when saidoperating member is moved to its first on position, the circuit betweensaid terminal members is completed and the heating circuit of said firstbi-metallic element is also completed, said first catch means sewing tomaintain said operating member in said on position until said firstbimetallic element heats suificiently to release said first catch meanswhereupon said operating member is moved by said resilient means towardsits off position, movement of sa d operating member into its offposition being prevented by said second catch means which arrests saidoperating member in its second on position wherein the circuit betweensaid first and second terminal members is again completed and theheating circuit of said second bi-metallic element is also completed,the switch being maintained in its second on position until said secondbimetallic element heats sufliciently to releasesaid second catch means,so that said bi-metallic elements together determine the overalloperating period of the switch.

2. A switch as claimed in claim 1 wherein in the on positions of theswitch the circuit between said terminal members is completed throughthe respective bi-metallic element.

3. A switch as claimed in claim 1 wherein said bi-rnetallic elements arecarried by said operating member and are electrically connected to oneof said terminal members, the other of said terminal members definingsaid clutch means and being engageable by said bi-metallic elementsrespectively in the respective on position of the switch.

4. A switch as claimed in claim 1 including means whereby the switch canbe cancelled manually before the end of said operating period.

References Cited UNITED STATES PATENTS 2,639,095 5/1953 Cubberley337-340 FOREIGN PATENTS 1,191,018 4/1965 Germany.

BERNARD A. GILHEANY, Primary Examiner B. M. MORGAN, Assistant ExaminerUS. Cl. X.R. 337-40, 78, 336

